I've just run into what I think is an oddity in type-casting. I have code similar to the following:
interface IMyClass { }
class MyClass: IMyClass { }
class Main
{
void DoSomething(ICollection<IMyClass> theParameter) { }
HashSet<MyClass> FillMyClassSet()
{
//Do stuff
}
void Main()
{
HashSet<MyClass> classSet = FillMyClassSet();
DoSomething(classSet);
}
}
When it gets to DoSomething(classSet), the compiler complains that it can't cast HashSet<MyClass> to ICollection<IMyClass>. Why is that? HashSet implements ICollection, MyClass implements IMyClass, so why isn't the cast valid?
Incidentally this isn't hard to work around, thought it's slightly awkward.
void Main()
{
HashSet<MyClass> classSet = FillMyClassSet();
HashSet<IMyClass> interfaceSet = new HashSet<IMyClass>();
foreach(IMyClass item in classSet)
{
interfaceSet.Add(item);
}
DoSomething(interfaceSet);
}
To me, the fact that this works makes the inability to cast even more mysterious.